The physical nature of the loop-top X-ray sources in the gradual phase of solar flares

We have analyzed Yohkoh soft and hard X-ray images of 36 flares, primarily to study the loop-top source that often prevails in these wavelengths durin g and following the impulsive phase. There are typically two patterns for t he location of the low-energy (15-30 keV) hard X-ray (HXR) source with resp ect to the soft X-ray (SXR) loop. In a quarter of the flares, the HXR sourc e lies in an extended structure separate from the brightest SXR loop. In ot her flares, the HXR source appears to be part of the same bipolar structure as the SXR loop, but its centroid is often displaced from the SXR loop-top source. The fact that the HXR source is not cospatial with the SXR source may reflect the presence of a distinct hotter structure. According to Yohko h X-ray emission-line spectroscopy, the similar to 20 MK plasma accounts fo r only a fraction of the HXR counts. The temperature maps obtained from the SXR broadband photometry occasionally reveal high-temperature areas outsid e the bright loop, but they also tend to be displaced from the HXR source, indicating that they do not represent the superhot (greater than or similar to 30 MK) plasma. We discuss possible distributions of plasma of different temperatures that could be consistent with the data.